The Art of Astroimaging

How to Get Started in CCD or 35mm Celestial Photography

Black Forest Observatory (pictured above) was Colorado's largest observatory,
period! It had been in existence for over 15 years (see User Installations
link, The Story of BFO for more info).
The telescope pictured above is BFO's computer controlled 30-inch Cassegrain
telescope, with 20" Byers drive, set up for astroimaging. The imaging
train equipment, shown in the above telescope picture from left to right,
is an old SBIG ST-6 CCD camera, a VSE remote controlled 2-inch [dual wheel]
filter wheel, an early custom 2.75-inch Flipper (with giant 2.75-inch format
eyepiece, shown on right side, and real-time CCD autoguiding camera in the
off-axis side port, shown on top of Flipper), and finally a massive 2.75-inch
remote controlled rack & pinion focuser. The second picture is BFO's
control center (warm room), with three computers networked together; one
for telescope positioning, one for image downloading, and the one on the
far right is for general reference (included in this database is the Palomar
Sky Survey on many CD-ROM's, over 100 professional astronomy books and sky
catalogs, including the Hubble Guide Star Catalog). Note BFO's 30" Cassegrain
through the warm room's viewing window.

Note: all caps above indicate a main section, cap on first letters [only]
indicate a sub-section

INTRODUCTION

For many experienced astroimagers, correctly installing an imaging train
on a scope and using the correct procedure to capture high quality images,
has become common sense. But we must also consider the novice, who has no
experience whatsoever in astroimaging. Therefore, this basic [quick and dirty]
introduction to astroimaging is provided for the beginner, who is very interested
in becoming an experienced astroimager, but has no idea where to begin to
learn the art [and subtleties] of astroimaging, or doesn't have the time
[or inclination] to read through all those "hieroglyphic" astrophotography
books with all those graphs and heavy math.

PROPERLY INSTALLING AN IMAGING TRAIN ON YOUR TELESCOPE

There are various pieces of equipment necessary to construct an imaging train
and, when properly stacked together (similar to railroad cars), give
you the capability to produce a quality astroimage in the least amount of
time, and with as little frustration as possible. There are many [adaptive]
ways to attach various accessories to different types of telescopes. We are
only going to discuss one simple, basic imaging train, because all the different
models and imaging accessories operate similarly. Once you've learned the
basics, they will apply to all the other imaging systems on the market. Some
will have more features, and be easier to operate, and others will be awkward
and frustrating but, after reading this compendium, you will be better equipped
to discern the "good stuff" from the bad.

One of the most common coupling formats is the 2"-24tpi male threaded found
on most SCT visual backs. This format was first introduced by Celestron,
and Meade Instruments soon followed with the same fitting (almost), which
has now become an industry standard in Schmidt-Cassegrain telescopes. Another
very common telescope coupling is the 2" female slide-fit [usually a focuser
input] that accepts 2" barrel-nose eyepieces and other accessories, and is
mounted on most Newtonian, refractor, and some types of Cassegrain telescopes
with their myriad of common optical configurations (i.e. Schmidt, classical,
Ritchey-Chretian, Maksutov, Dall-Kirkham, etc.). The equipment's female threaded
slip-ring attaches to its 2"-24tpi male counterpart on the telescope's visual
back, and offers a very short profile and excellent security. It was primarily
designed to support extended astroimaging trains in the days of 35mm
astrophotography, but has been easily adapted to CCD astroimaging. This format
does not easily allow for field rotation. It was primarily designed for visual
eyepiece observing, but has been extensively utilized to secure imaging trains
because it was simply there at the time. In hindsight, no barrel-nose format
should have ever been used for imaging train applications because it wastes
profile (except when inserted in a focuser) and can't be properly secured
with one or even two thumb screws, thus the necessity to develop VSE's new
Quad-Lock system which allows the barrel-nose format to be as rigid and secure
as any threaded format. However, this barrel nose format does allow for easy
field rotation (addressed later). The 2" slip-fit barrel-nose format can
be made more secure (but not more rigid) by providing a 1/2" long [or so]
machined security indent in the male barrel tube. This provides a recessed
section in the barrel in which the thumb screw(s) can reside. Even if the
thumb screw(s) come loose, the equipment cannot detach itself from the telescope,
and cause a catastrophy.

Installing a Secondary Focuser on your Telescope

The novice will think that a secondary focuser is an option he really can
do without. He may be right, but not usually. With rare exceptions, most
commercial Schmidt-Cassegrain telescopes (SCTs) require a secondary focuser.
Secondary focusers are designed for the current generation of Meade/Celestron
Schmidt-Cassegrain telescopes that focus by moving their primary mirrors
and accept accessories via their standardized threaded visual backs. The
four SCT standards are 2"-24tpi for both Meade and Celestron (using a reducer
for the 10" and larger models), 3.25"-16tpi for Meade (10" and 12" models),
3.29"-16tpi for Celestron (11" and 14" models), and 4"-16tpi for the Meade
16" SCT.

Without a secondary focuser, a serious problem arises when you try to focus
using the focusing knob protruding from the SCT's visual back. Your image
will begin to shift laterally around the field of view - very frustrating
indeed. Small amounts of image shift are acceptable when casually viewing
the celestial sky through even a moderately high-power eyepiece, but when
you attach an imaging train to your SCT and try to center a guide star in
your eyepiece's illuminated reticle crosshairs, etc., you find that this
mild irritation has become intolerable. The image jumps all over your image
plane and field of view. You have just encountered unacceptable lateral image
shift. Until Meade and Celestron start building a better SCT (yes, you can
eliminate the lateral image shift by simply designing and implementing a
better fork-type primary focusing arm), the astroimager must use a secondary
focuser docked to the SCT's visual back to eliminate the focusing wiggles.
Even if there was no lateral image shift, SCT's move their primary mirrors,
which provides a focusing ratio that is approximately 6 times as coarse as
other types of common secondary docking focusers. Therefore, rock-solid
micro-focusing becomes a very useful upgrade even without lateral image shift.

Since your SCT's primary focusing system manages all your large
focusing position changes, your secondary focuser need not
have more than about 0.1" of actual overall travel. In reality, most secondary
focusers have much more focus range (all VSE MasterGlide focusers provide
a full inch of redundant travel and our MicroGlide focusers provide 1/2-inch).
You attach a secondary focuser to your SCT by simply screwing it onto your
visual back (Note that MasterGlide focusers utilize the larger, more rigid
3.25"-16tpi large format threaded visual back for Meade 10" & 12" SCTs
with a 4" adapter available for Meade 16" SCTs, and a 3.29"-16tpi adapter
for Celestron C11, C14). You then insert an eyepiece or diagonal, etc.
into the focuser's input as you would with any other standard focuser. VSE's
2" Threaded Barrel Adapter (item #A2LT) can easily
be inserted in a MasterGlide or MicroGlide focuser's moving tube and rigidly
affixed using Quad-Lock. This converts the output to a rock-solid 2"-24tpi
male format so you can utilize all the standard, commercially available
accessories and extended imaging trains.

The upper right picture illustrates an imaging train composed of VSE components.
The straight-through imaging train consists of a [now discontinued] VSE Filter
Wheel (FW4) + Super Power Focuser [also discontinued,
but replaced by the MasterGlide M5] + Slider 2 + 35mm SLR camera (which could
easily be substituted for a CCD camera in a matter of seconds since both
camera formats now use the same T-thread fittings). A 40mm Televue wide-field
eyepiece has been inserted in the Slider's top slide-mirror port, and a VSE
25mm illuminated reticle guiding eyepiece (also discontinued because we finally
ran out of military-surplus glass reticles) has been inserted in the
side pick-off port. It doesn't get much better, or easier, than this! And
you thought I forgot expensive! Nope. You could cut the expense to a small
fraction of the above imaging train by utilizing one of VSE's less expensive
focusers (i.e. M1, M2 or MGF, etc.) and a Slider using it's [FREE] built-in
2" format filter slot and accomplish the same end imaging result without
all those high-dollar "bells & whistles" which are typically used for
total remote operation from observatory warm rooms, etc. VSE also offers
in-line Filter Slot Adapters, or our Filter Slide System (see
Filter Adapters link).

Installing a Focal Reducer on your Secondary
Focuser

The second imaging train accessory we're going to discuss is the focal reducer
(pictured at right to scale, full size, depending on your monitor's resolution
of course). The focal reducer used to be a necessity when imaging with CCD
cameras with relatively small imaging areas, compared to 35mm formats. A
focal reducer and CCD camera combination can approach the larger field offered
by 35mm cameras without a focal reducer. When the CCD imaging industry first
came on board, the chip size wasn't much larger than a gnat's butt, and it
was almost impossible to acquire a bright star on the [microscopic] chip
area, let alone a faint deep-sky object. Today, CCD chips have dropped
dramatically in price, and increased [literally exponentially] in area. These
new larger chips are now approaching the size of 35mm format, negating the
need for a focal reducer altogether, and the optical distortions caused by
shortening your light cone and passing it through all that glass. Simple
prime focus is always the best way to acheive the best images, but focal
reducers can still be used effectively for wider-field imaging.

If you have a Meade/Celestron Schmidt-Cassegrain telescope, you just screw
their respective f/6.3 focal reducer onto the 2" threaded male visual back
of your SCT. If you have a telescope with a standard 2" slide-fit focuser
that accepts 2" barrel-nose stuff, you need to purchase one of VSE's 2" Threaded
Barrel Adapters (see ADAPTERS link). You then screw
the 2" Threaded Barrel Adapter (Item #A2LT) into
the female end of your focal reducer, and insert that combination into your
2" slide-fit focuser and lock down the thumb screw(s) into the recessed indent
in the male tube. Now you have a 2" male threaded fitting available on which
to screw a Slider (with the 2" threaded female slip-ring input). Of note,
using a focal reducer should be avoided if at all possible, unless you like
to immerse yourself in a "bag of worms."

Consider VSE's exclusive focal reducer "hidden cavity" super feature located
inside the moving tube of all MasterGlide focusers. Instead of installing
a focal reducer (FR) conventionally, and consuming all that valuable
profile, you install it inside the focuser's moving tube and save your profile
for other imaging train accessories. It also moves the FR closer to the SCT's
visual back where it was originally intended to be installed. All Meade/Celestron
f/6.3 focal reducers fit inside the MasterGlide focuser's moving tube. The
f/3.3 focal reducers, utilized in the MasterGlide's "hidden cavity," are
too fast to be practical in most extended imaging train applications, unless
you are simply inserting an eyepiece or camera directly into the focuser
itself.

You have, or are considering the purchase of, a CCD camera with a built-in
guiding chip, or a CCD camera that has an imaging chip with an area that
can be dedicated to guiding, so you don't need a Slider. Think
again! You think it's easy to find a suitable guide star with
a fixed separate guide chip, or a fixed chip area dedicated
to guiding? Are you, or would you like to be, a masochist that likes guide
star frustration? Since your guide chip [area] is integral and fixed, your
ability to scan for an adequate guide star is diminished by a factor of ten,
compared to the Slider's easily adjustable independent pick-off mirror. Even
with your fancy dual [fixed] chip guiding/imaging CCD camera, guide star
acquisition can still be a literal nightmare if you don't have a way
of positioning a guide star independent of your imaging target. This is the
capability a Slider offers. Of course, you need to use a separate guiding
CCD camera, or guiding eyepiece, allowing you to simply scan for a guide
star and pick & choose any usable star in or around your target object.
This is accomplished by simply rotating the Slider itself (Z-axis). Yes,
you can also rotate a CCD camera, but you are still limited to a fixed area
of rotation without the necessary independent X-Y axis adjustable pick-off
mirror controls of the Slider. Once you've acquired a usable guide star,
it's quick and easy to center, or place, any star in the Slider's pick-off
field in 2 seconds or less. Consider the new
Starlight Express
SXV-H9C with the separate guiding camera that slips right into the Slider
2's [1.25" format] off-axis guiding port - a marriage literally made
for heavenly imaging!

Installing your Sidewinder

Understand that a standard focal reducer will not install on the Sidewinder's
front input port. You need to install it on the rear port just before your
camera. If you do this, you will need to extend out all the lateral ports
about 6" to achieve parfocus. If you have a few extension drawtubes or diagonals,
they will do the job. This means that any focal reducer is not recommended.
If you have a chip that is larger than 35mm format, you really don't need
a focal reducer that adds glass and other imperfections. Your scope's light
cone should remain pure to achieve the best imaging results. This is an opinion
that others may disagree with. Also, Sidewinders will not work with any 2"
format focuser, including VSE MasterGlide and MicroGlide focusers. However,
the Sidewinder will install on the output of our MicroGlide Coupling Focuser
(Item #MGFCO), which has a larger input and output
thread, with a 2.25" internal clear aperture. Next, screw your Sidewinder
(using the proper docking port ring) onto your scope. You can screw the docking
port ring onto your scope, then slip the Sidewinder over the ring and tighten
the three set screws, if you wish. With your Sidewinder rigidly affixed to
your scope, you will [next] need to install your 35mm or CCD imaging camera,
to the rear output port of the Sidewinder (discussed below). For additional
info, also see VSE's Imaging Train Configuration
link.

You have, or are considering the purchase of, a CCD camera with a built-in
guiding chip, or a CCD camera that has an imaging chip with an area that
can be dedicated to guiding, so you don't need a Slider or Sidewinder.
Think again! You think it's easy to find a suitable guide
star with a fixed separate guide chip, or a fixed chip area
dedicated to guiding? Are you, or would you like to be, a masochist that
likes guide star frustration? Since your guide chip [area] is integral and
fixed, your ability to scan for an adequate guide star is diminished by a
factor of ten, compared to the Slider or Sidewinder's easily adjustable
independent pick-off mirror. Even with your fancy dual [fixed] chip
guiding/imaging CCD camera, guide star acquisition can still be a literal
nightmare if you don't have a way of positioning a guide star independent
of your imaging target. This is the capability a Slider or Sidewinder offers.
Of course, you need to use a separate guiding CCD camera, or guiding eyepiece,
allowing you to simply scan for a guide star and pick & choose any usable
star in or around your target object. This is accomplished by simply rotating
the Slider or Sidewinder itself (Z-axis). Yes, you can also rotate a CCD
camera, but you are still limited to a fixed area of rotation without the
necessary independent X-Y axis adjustable pick-off mirror controls of the
Slider and Sidewinder. Once you've acquired a usable guide star, it's quick
and easy to center, or place, any star in the Slider or Sidewinder's pick-off
field in 2 seconds or less. Consider the new
SBIG STL-11000, 11 Megapixel CCD camera.
In fact, SBIG's STL was the catalyst for VSE's Mega-Port Sidewinder - the
time had come! Use the STL and Sidewinder in combination with SBIG's STV
and you've assembled a dream machine that will easily create "frustration-free"
professional astroimages worthy of the largest observatory on Planet Earth
and beyond.

Installing your CCD or 35mm Camera
on your Slider

First we will discuss the installation of a CCD camera as your final item
in your imaging train. All modern CCD cameras, such as the SBIG, Starlight
Express, and Apogee lines of excellent CCD imaging cameras, now have a standard
42mm female T-thread input coupling, not like the old-style 1.25"
barrel-nose ST-6 CCD camera pictured at right. Providing your CCD camera's
input has female T-adapter threads, you will use VSE's Zero Profile T-Adapter
(ZPTA, item #AZP2T) between the Slider's rear
port and your imaging camera. If you are going to use a 35mm camera
for imaging, just screw a T-ring adapter, that is specifically designed for
your particular brand of 35mm camera (i.e. Nikon, Minolta, Olympus, Pentax,
etc.), onto the Slider's ZPTA in the rear imaging port. If you have a Slider
2 with the side pick-off port, you should position your camera in the
vertical position which will put the long [skinny] side of
the rectangular film further away from your pick-off mirror and lessen the
vignetting on your film caused by the pick-off mirror's protrusion into your
telescope's light cone. If you have a rectangular CCD chip, this procedure
also applies.

Since your 35mm camera focuses about 1.5" further in than a CCD camera, you'll
need an extension drawtube out the top slide-mirror port and the side pick-off
mirror port to parfocus your system. You may think that this 35mm camera
procedure is awkward, but it's much better than extending/wasting your profile
for CCD cameras. To explain, most other flip-mirror devices on the market
extend the rear port to parfocus for CCD cameras. The superior Slider method
of parfocusing always maintains the shortest straight-through profile whether
you're using CCD or 35mm cameras. Just remember, CCD = no extension drawtubes,
35mm = extension drawtubes with Sliders. We'll talk further about parfocusing
your Slider between 35mm and CCD in "Paul's Pictorial Parfocusing
Primer" below, and the subject is also discussed at the Questions &
Answers (FAQ) link on VSE's home page.

PREPARING YOUR IMAGING TRAIN FOR
ASTROIMAGING

Illustrated at right is a partially assembled imaging train (less secondary
focuser to simplify), as discussed above, docked to a Meade 8" LX200's visual
back, a good astroimaging entry level scope. You will also need to insert
a very low power 2" format eyepiece (pictured is a 2" format 40mm eyepiece,
see FYI below) in the Slider's top slide mirror port, and a higher power
1.25" format illuminated reticle guiding eyepiece in the side pick-off port.
You can use any of the commercially available guiding eyepieces on the market.

FYI, a field lens (sky side lens) that is the full internal diameter of
the 1.25" tube is the widest true field achievable in that specific format.
Example: A 1.25" 40mm eyepiece doesn't have a wider true field than a 32mm
eyepiece. A 1.25" 40mm eyepiece will achieve a lower magnification, but achieve
the same true field as the 32mm eyepiece with no increase in true field.
This causes the 40mm eyepiece to seem like it is losing apparent field compared
to the 32mm eyepiece, creating a "tunnel vision" view through the eyepiece.
This field relationship applies to 2" format eyepieces too. The maximum true
field tops out at about 55mm in 2" format.

First you need a good brisk, clear night with above average "seeing" conditions.
You can test "seeing" by imaging a finite solar system object or a bright
star (splitting double stars is a good test too). If the object looks like
it is boiling, and/or appears to have a lot of chromatic scintillation (color
shifting), I would wait for an atmospherically calmer night, or you can use
a bad "seeing" night to practice.

After you've leveled and polar aligned your scope (explained in the manual
that came with your scope), you need to decide which object you would like
to image first. I would start with relatively bright summer deep sky objects,
such as the Ring Nebula (M57) in Lyra, or the globular cluster in Hercules
(M13). If it's winter, try imaging the Orion Nebula at the tip of Orion's
sword, although it may be a little too large for CCD cameras with smaller
chips. You can also use an open cluster, or a brighter star field, to test
your imaging system. But before you try to locate an object through your
scope, push the Slider's slide mirror knob all the way in. That puts the
angled 45 degree slide mirror in the path of your incoming light cone, and
sends the cone to the top slide mirror wide-field eyepiece. Do not
use high power eyepieces in the Slider's top port when trying to
image. That port is specifically designed for lower power field-finding
eyepieces only (explained in-depth later). Of course, any power eyepiece
will work in the top port. The Slider or Sidewinder make great diagonals
for visual observing, when you're not trying to acquire an object to image.

Focus your telescope, by looking through the Slider or Sidewinder's top port
LOW power eyepiece, on a low to medium brightness star (10th
to 5th magnitude) near the object you are going to image. Do not focus on
a star halfway across the sky from where you plan to image. Also, re-focus
your imaging camera when moving to another object that is [let's say] more
than 20 degrees from where you are currently imaging. You need to do this
because all telescopes have mechanical flexure, caused simply by gravity,
that can de-focus your telescope and shift your telescope's field center
by many arc seconds, to possibly a few arc minutes, as you move your telescope
across the sky. Once you have that star in focus, and centered in your
eyepiece's field of view, you need to focus your imaging camera. Don't forget
to pull the Slider's mirror knob out so your imaging cone is redirected
straight-through to your imaging chip. With a CCD camera, and the specific
software that came with your camera, you can manually focus using the software's
focusing sub-routine, or use your autofocus sub-routine in conjunction with
an autofocus equipped focuser. When you have the smallest pixel count possible,
you're CCD camera is focused and ready to take a time exposure of your deep-sky
object. Never try to focus any imaging camera by looking through an
adjacent eyepiece! More on this important focusing subject latter.

Paul's Pictorial Parfocusing Primer

Say that three times real quick. Betcha can't without spitting all over yourself?
Anyway, I hope this section will provide you with a better understanding
of parfocusing any imaging train, not just the Slider
used in this compendium. I selected the [long] discontinued Micro-Slider
(MS) and Flipper because they are designed to parfocus "in-reverse" of each
other, which should provide you with a better concept of parfocusing principles
(oops! there's another P-word). The MS parfocuses, from 35mm to CCD camera,
by adding length to the straight-through imaging port (noted in red, upper
left) which is the most inefficient method of parfocusing (like the Meade
flip-mirror devices) because you are increasing your imaging train's profile
- that's a NO-NO! The Flipper and Slider parfocus, from CCD to 35mm camera,
by adding drawtubes to the top port (noted in red, lower right) and side
pick-off ports (not shown), which is the most effective method to parfocus
your imaging train. Because you are not adding length to your existing
straight-through profile to parfocus your system, it remains the same for
either CCD or 35mm cameras. Remember that a shorter imaging train is
always preferred because it's simply more solid, eliminating system flexure
problems as you move from object to object.

Typically, with a CCD camera, you will not need an extension drawtube
using a Slider or Sidewinder (see lower left Flipper), because most CCD cameras
are roughly parfocus with most newer standardized eyepieces. However, with
a 35mm camera, that focuses about 1.5" further out from a standard CCD camera,
you will need an extension drawtube (Item#AD22S
or AD21S for Sliders) between the top port
and your eyepiece (see lower right Flipper, area in red). Of note, Meade
has adopted the inferior reverse design on their flip-mirrors that extends
the imaging train profile instead of the top, bottom or side mirror port
profile like the Sliders and Sidewinders. To further reiterate, note the
two lower Flippers above. The red area noted on the lower right Flipper
illustrates an inserted drawtube that is needed to parfocalize your system
when using a 35mm camera, and is not needed when imaging with a CCD camera
(see lower left Flipper). Conversely, the upper two Micro-Sliders obtain
parfocus by extending the CCD camera's straight-through profile (again, a
no-no) noted in the red area in the upper left Micro-Slider image.

A 35mm camera is a little more difficult to focus because what you think
is in focus, when you look through your SLR camera's viewfinder (onto the
ground glass image plane), is usually out-of-focus just enough to give you
a soft or slightly fuzzy picture. The best way to make absolutely sure your
35mm camera is in perfect focus is to use an after-market focal plane focusing
device (i.e knife-edge, grating, etc.), like the one pictured at left. There
have been different types available that incorporate knife edges, split images,
double images, Ronchi gratings, etc. Celestron offered, what they called
an MFFT-55 (Multi-Functional Focal Tester-55), that would evaluate
a telescope's focal plane for focus, collimation, and curvature of field,
but have discontinued it long ago. With the decline of 35mm imaging and the
increase of CCD imaging, these devices are becoming less and less common.
There is still one very high-quality device currently on the market.
Stiletto Image Focusers from
STI offers many 35mm and CCD focusing devices.

The illustration at right represents
a too far in, too far out, and perfectly focused image as seen through a
knife edge type, focal plane focusing device. Illustration 1 represents
a shallow focused gradient image produced by the knife edge that moves across
the field from left to right. Illustration 2 represents a deep focused
gradient image produced by the knife edge that moves across the field from
right to left. Illustration 3 illustrates a perfectly focused image,
as the field instantaneously goes to dark across the entire field of view.

Don't be fooled by claims that you can obtain quick, accurate, pin-point
camera focus from a flip-mirror device using a secondary high powered, helical
focusing eyepiece, because you can't. And don't ever try to achieve critical
focus through your SLR's viewfinder (it's real hard on your neck, too). There
are similar looking devices (like Sliders) out there that indirectly imply
you can achieve critical camera focus with a high powered eyepiece in the
top flip-mirror port. Not possible! First, you can't achieve critical
[sharp] focus using a high powered eyepiece in any device's top flip-mirror
port (explained in the next paragraph). Second, how are you going to locate
your imaging target through a high powered eyepiece with no field of view?
This type of device looks spectacular to the novice, but in reality is quite
dysfunctional when trying to acquire your sky object and achieving final
critical focus.

You should always use a "non-eyepiece" focusing method to achieve final critical
focus, like an after-market focal plane focusing device (such as the ones
discussed a couple of paragraphs up), or your 35mm astroimages will typically
turn out fuzzy and/or soft. Oh, you might "get lucky" with an image, from
time to time, but is it really worth all that effort to get lucky, or would
you rather spend a little more time using an aftermarket focusing device,
and be guaranteed tack sharp super astroimages every time? To reiterate,
helical focusing using multi-imaging portals (MIPs) is completely unnecessary.
The standard distance, from the front face of your T-ring to your SLR's film
plane, is precisely 55mm. The human eye simply can't perceive and focus on
that critical distance by looking at an image directly through the eyepiece.
It is impossible, especially when that accuracy must be precisely 55mm, not
55mm plus or minus 1mm (which is 0.04").

Think about this simple lesson in common sense. Your eyes are never
perfectly "in-focus." Even if you are diagnosed with 20-20 vision, critical
camera focus is not achievable with your eye, because there is no such thing
as perfect 20-20 vision. Many people wear glasses to correct focus imperfections,
and from year to year an eyeglass wearer needs to get his eyes examined and
new glasses with a different Rx, because your eye's focus point on your retina
has changed. Your eyes will be changing for the rest of your life. Every
eyeglass wearer has tried looking through a telescope with, and without,
his glasses. The eyeglass wearer had to drastically change the telescope's
focus each time. So how can you possibly try to achieve critical camera focus
with your eye - it is literally impossible! Especially with an astigmatism,
which afflicts half the people in the world. The above has been confirmed
by conversations with Dr. Dale Anderson, MD, PC, who is an ophthalmologist
and noted eye surgeon.

There is one particular [current] misleading ad in S&T magazine that
says, and I quote, "Focus through your eyepiece." Focus what? Your eyepiece
for your eye's sake? Yes, you can do that. Your camera? Definitely not! If
this statement is telling us that all telescopes focus through their eyepieces,
then I think even the novice has figured out that basic concept long ago.
If not, then the true implication can only be interpreted to deceive. This
deceptive advertising is deliberately leading the novice [want-to-be] astroimager
to believe that he can simply focus his CCD or 35mm camera, using his eye
and an eyepiece, at the focus of their flip-mirror device. If you are one
of those people who have been lead to think this, then I hope you appreciate
this basic reality check. Designing an imaging train around this misconception
could have [or may already have] lead you down the wrong path.

If it isn't exact, your images will always turn out to be mediocre, instead
of celestial masterpieces worthy of enlargement and framing. You will sacrifice
those special moments in time, when you can proudly say to your friends,
"I took that picture!" And they'll say, "WOW! That picture looks like it
was taken at one of the big research observatories." Sure, it's a little
more effort to remove your 35mm camera from the telescope, and screw a focal
plane focusing device on to the Slider or Sidewinder's rear T-adapter port.
Then, after you have achieved optimum focus, unscrewing the focusing device,
and carefully reinstalling your 35mm camera onto your scope. But you don't
have to go through that procedure for every image, unless you move your scope
to a completely different area of sky. Remember the flexure problem discussed
a couple of sections up. And, that extra effort is a lot less time consuming
and frustrating than trying to switch between high powered [no-field] and
low powered [wide-field] eyepieces to find your target object.

From over a decade of imaging experience at Black Forest Observatory, we've
found that using wide-field eyepieces for image locating in your top
port, with simple push/pull secondary focusing (on all Sliders and
Sidewinders) is much quicker and more efficient than any redundant helical
focusing system (all Sliders offer full aperture top port mirrors for those
wide-field eyepieces). You're actually wasting that top port, on a function
that can't be achieved, when you could be using that top port for other purposes.
Your secondary eyepieces (top port wide-field and side port guiding) can
simply be "ball park" focused, because your eye doesn't need [and can't see]
that critical focusing difference anyway. The only critical focus is at the
camera. With these procedures, your camera's image will always be guaranteed
tack sharp, and that's the bottom line, period! BTW, VSE does offer a helical
focusing drawtube insert (see ADAPTERS link) as a
convenience accessory if you want one.

FINALLY, TAKING THE FIRST EXPOSURE THROUGH YOUR IMAGING
TRAIN

Let us assume that you have already gone through the effort to pin-point
focus your CCD or 35mm (using a focal plane focusing device discussed above)
camera on a nearby star, and have aimed your telescope at a neighboring deep
sky object, after parfocusing your top port's wide-field eyepiece with your
imaging camera (Oh, if I forgot to mention this earlier, parfocus simply
means that your camera and eyepieces are focused at the same point). Once
this object, let's say the Ring Nebula in Lyra (M57), is centered in your
parfocused wide-field eyepiece, go to your Slider or Sidewinder's side pick-off
port's guiding eyepiece and parfocus that next, on an appropriately bright
guide star. If you're lucky, you'll have a guide star in your guide eyepiece's
field of view, and you can just center the star using the techniques explained
below. If you don't see a suitable guide star in your guide eyepiece, you
will need to acquire a guide star out-of-field. You do this by simply turning
the Slider's little black knob (loosen the knurled lock knob first), or
Push/Pulling the Sidewinder's insert in and out, across your light cone's
lateral X-axis. If this doesn't acquire an appropriate guide star, then move
the Y-axis lever protruding from the top of the Slider's side port, or rotate
the Sidewinder's insert. This action will rotate the pick-off mirror effectively
providing a perpendicular axis of adjustment. These two controls provide
X/Y-axis, 360 degree micro-positioning of the internal pick-off mirror and,
9 chances out of 10, this simple [exclusive to VSE] procedure will acquire
a usable guide star. If not, then you can obtain a third axis adjustment
(I call it the Z-axis) by rotating your Slider or Sidewinder in a circular
motion, either by loosening the thumb screws in your 2" focuser and rotating
your Slider, or rotating the Sidewinder on its threaded input docking
port. It is advisable to rotate the Slider or Sidewinder body only a
few degrees at a time, since your guiding eyepiece usually has less than
a one degree field of view. Then do your X/Y-axis "scan" again. Once you've
acquired and centered a suitable guide star in your guiding eyepiece, you're
ready to start the exposure (either 35mm or CCD camera). For 35mm camera
imaging, you'll need one of those extension shutter release cables that have
a built-in lock. For CCD imaging, just go to your computer to start the exposure.
Don't forget to pull the main mirror out slowly and carefully, to remove
the diagonal mirror that is blocking the light cone's straight-through path
to your imaging camera. Hopefully, your image will already be perfectly focused
on the film plane in your SLR camera (see above for camera focusing procedure).

Eyepiece Guiding on a Guide Star

We're only going to discuss manual eyepiece guiding, except for the following
brief note, because all the information you should need is usually in the
CCD guiding camera's instruction manual. When using a CCD guiding camera,
the set-up procedure is almost identical except, when you've acquired and
centered a guide star in your guiding eyepiece, you carefully remove that
eyepiece, and replace it with the CCD guiding camera. Guiding on a boiling
stellar dot, in a guide eyepiece, for long periods of time, can get quite
physically fatiguing, not to mention eye strain. Bilberry Extract, available
at your local health food store, is said to help your night vision, and help
relieve eye strain from long guiding sessions. Try to keep your guide star
in the corner of two perpendicularly opposed illuminated lines, and use a
comfortable chair/stool. Don't guide standing up, because when you lose your
equilibrium, and fall over in the dark, you really don't know what your going
to fall on in those farmers' fields. It could get really ugly and messy
down there. That way you can catch a drift almost instantly, and correct
for it with your drive controls, before your imaged stars become "squiggly
things." Eventually, you will learn your local sky's exposure duration, before
your film/chip begins to fog from background light pollution. You will find
that a properly aligned mount will nearly eliminate any drift in declination,
so correcting in DEC will not be as frequent as correcting in right ascension.
You see, worms (the small diameter helical cut gear, with the drive motor
attached to one end of its shaft, that drives your RA shaft's larger diameter
gear, at an angle that is perpendicular to itself) can't be manufactured
to be perfectly concentric or symmetrical. They always end up with eccentric
or asymmetric rotational errors, because even the most accurate lathes or
milling machines in the world still can't eliminate the worm's imperfections.
Ed Byers made the lowest periodical error RA drive systems available for
commercial telescopes, because he had those very expensive, and accurate,
"tenth" milling machines ("tenth" is machine shop slang for 1/10,000th of
an inch). You will always have to deal with periodic errors induced by the
worm, unless you don't drive with a worm.

If you have a PEC (periodic error correction) system on your scope, don't
forget to calibrate that system. It can reduce your guiding to a minimum.
It's also a great "bandaid" for all those low accuracy, high periodic error
worm gears that Celestron/Meade put in their scopes. Some even install spur
gears on their RA shafts in conjunction with helical cut worm gears. These
"non-meshing" worm/spur gear systems are designed only for casual eyepiece
viewing, not astroimaging. Make sure your scope has a true worm gear drive,
not a sloppy fitting spur gear system.

If you process your images in a computer, using Adobe Photoshop, etc., you
can usually go past your fogging limit without damaging results, because
you can process the image faults out of existence. I use Photoshop 7 to create
VSE's display ads for Sky & Telescope magazine, and all those gaudy graphics
you see at VSE's web pages. The software's capabilities are near unlimited,
and the unsharp mask feature is very valuable for sharpening sky images.
What you can create in your mind, you can transfer to screen/paper. Your
only limitation is Photoshop's steep learning curve. I've been using Photoshop
since version 2 (that's many years), and I haven't touched on many of its
features.

35mm CAMERAS & FILMS FOR
ASTROPHOTOGRAPHY

If you have one of those fancy "automatic" SLR cameras, leave it in the closet.
You need to have an old "totally manual" SLR camera with a bulb setting,
and definitely without auto-film advance. Could you imagine using an auto-advance
camera for astrophotography? Your shutter lock slips, and your camera advances
to the next frame. Bzzzzzzzzz! It could even wake you from your celestial
nap! The best camera I've found, and use at BFO, is the Nikon F2 with the
removable top, prism viewfinder. You could also easily remove the old ground
glass focal plane, from underneath the prism viewfinder, and replace it with
a Beattie Intense Screen (4 times the brightness of conventional ground glass
focal planes). We use a Beattie Intense Screen (available through the camera
merchants who advertise in the back of S&T) in BFO's Nikon F2. You can
insert a homemade block (made of soft aluminum or hardwood) in the camera's
empty rectangular viewfinder hole. The homemade block should have a 1.25"
hole in the center, for the insertion of a low power eyepiece, that
has a primary focus about a half to 1-inch below the 1.25" format bottom
cylinder (either a push/pull fit or set screw would hold the eyepiece
secure in the plate). This installation would provide comfortable
right-angle viewing and coarse focusing through your SLR's viewfinder,
with or without a Beattie Intense Screen. It could even have interesting
applications beyond astroimaging. At minimum, it would be a useful, and fun,
construction project.

Some good films for astrophotography are Fuji print film or Fujichrome (slides)
400ASA, or higher. Kodak's 1000ASA films are quite grain-free compared to
a few years ago. If you would like to experiment with gas hypered films,
which increase the film's sensitivity to light and lower the film's reciprocity
failure, you can purchase that special film through Lumicon, listed in the
advertiser's index in the back of any S&T magazine. They even have a
gas hypering kit, so you can create your own gas hypered film.

FILTERS FOR 35mm & CCD ASTROIMAGING

There are many different filters available that will drastically improve
your astroimages. Besides the standard RGB (red, green, blue) filters, there
are some exotic filters available for 35mm black & white films, like
fine grain Tri-X and Plus-X, for color films (discussed above), and even
CCD imaging cameras. Again, most of these special filters are available from
Lumicon. For all types of astroimaging, you can get improved results by using
Lumicon's exclusive Deep-Sky filter, that will dramatically darken the stellar
background, and help to block light pollution. For B&W films, a minus
violet filter will give you pin-point stars. An H-alpha pass filter will
increase the visual range of your film into the infrared end of the spectrum.
However, this filter has a very severe application limitation; it only works
with B&W 2415 film. Since CCD cameras are very sensitive in the infrared,
you can purchase an IR Block filter to obtain more natural looking images
in the visible part of the spectrum. To obtain good 35mm color images, you
can just use color film, but if you want your colors to decisively stand
out, you can use a set of RGB filters, and take three separate images with
B&W film. You could even obtain a 4th separate image layer with an H-alpha
pass filter, to extend your red into the infrared, but you could only use
2415 high resolution film to take advantage of this 4th image layer. The
RGB multiple image filter array can just as easily be used with any CCD camera
too. Just name your images redm57, grnm57, blum57, etc. With B&W films,
you scan your processsed prints (or negatives, with a slide scanner) to create
a computer file of each color. Then create layers in Photoshop of each
color, combine them and flatten the image into one image, and you've got
a superior color image using B&W film.

My recommendation is to purchase all 2" filters. They may cost a little more,
but you can use them with larger CCD chips and 35mm films. 1.25" filters
have become obsolete because larger CCD chips and 35mm format films are too
large for the smaller filters and will vignette your images. All Sliders
are equipped with a built-in, very low profile 2" filter slot.

A BRIEF HISTORY OF TIME (my time, not Stephen Hawking's)

In the early days of astroimaging, guide scopes were extensively used to
track stars for astrophotography, but they found that guide scopes inherently
produced unacceptable system flexure that was very difficult to eliminate.
To reduce this flexure, heavier tubes, truss assemblies and mounting brackets
needed to be used, adding great expense and weight to the telescope. FYI,
guide scopes are still extensively used in Japan and the Orient, one of the
world leaders in amateur astrophotography per capita. That's why Takahashi
(Japanese) refractors, you purchase in the US, had no back focus. Takahashi
is just now "Americanizing" the refractors they import to the US (see the
new TOA-130 at the Installations link). Then came off-axis guiding,
but it was a frustrating literal nightmare to find a suitable guide star,
because the off-axis prisms were very small and fixed. Adjustable off-axis
aids were then introduced, but they too were very difficult to adjust, requiring
you to loosen thumb screws and move various mechanisms back and forth.

Then came Sliders and Flippers (now discontinued). They evolved from a simple
beginning. The need for practical, efficient, and effective ways to acquire
astroimages. There was nothing but awkward, unusable, devices on the market
back then. The only alternative was to manufacture our own multi-imaging
portals (MIPs) at BFO's machine shop. After many years of beta-testing and
experimentation, the Slider and Flipper design was finally perfected, but
for many more years, it was only used internally at BFO. Then, after ten
years, and much coaxing from my astronomical friends, I decided to manufacture
and market a production model at BFO's machine shop. And today, VSE creates
a revolutionary product line that is "second-to-none." Only the "pocket book"
or the erroneous purchasing choices of the novice provide VSE with any
competition.

CONCLUSION

After reading the above, these procedures
may sound like a lot of work and a very steep learning curve for the beginner,
but after you've purchased and set up your equipment and captured a few images,
it'll seem like second nature. And, most important, you will have bypassed
most of that astroimaging frustration, and put the fun back in this wonderful
celestial hobby. Unfortunately, many "would be" astroimagers have wasted
thousands of dollars because they simply don't research the subject, or take
the time to find [or purchase] the best products. People think that because
a product is advertised in a reputable magazine, it has to be a good, functional
product. Not true! You'll eventually thank yourself for taking the initial
time to find, and read, this compendium. Remember, VSE products are based
on functional simplicity, not a bunch of dysfunctional baubles. Examples
are: 1) separate filter wheels that waste important profile and add flexure
to your imaging train; 2) critical focusing devices where none are needed;
and 3) claims of pin-point focusing with the human eye which can't be done.
Now, you know better after reading the above, don't you. The simpler
[and shorter] your imaging train, the more efficient it will be, and then
you're on your "skyway" to becoming a reputable, world-class astroimager
(see Astro Links to visit some of these web sites).

I have tried to simply present "tried and true" logical imaging facts that,
I think you will agree, are justifiably stated. I want to use my expertise
to save my astronomical friends and colleagues the time, expense, and frustration
that can be found in astroimaging. Following the wrong path [to an end] can
disappoint many people, and discourage them from pursuing their astronomy,
space exploration, and astroimaging goals. We need all the [what I call]
pro-space citizens we can acquire, if we are to save the Planet for future
generations of yet unborn billions that need to survive on this speck of
dust in the universe (see Why Space? for more
"soapbox" stuff).

So, print this compendium, find a comfortable chair to go over the finer
points, and enjoy the "read." Keep this reference with your imaging equipment
until the astroimaging experience becomes a conditioned response, and don't
forget to make copies available to your astronomy club members who are interested
in astroimaging. Or reprint it in your club's newsletter, in sections (part
1, part 2, etc.) of course. I wish I 'd had this kind of basic information
when I began my astronomy efforts, but back then, the wheel hadn't been invented
yet, either.